Filters are optical elements with specific spectral transmission characteristics. They are used to modify the properties of a light source or to block unwanted wavelengths of light.
There are two different types of filters, depending on the physical principle exploited during the manufacturing process: absorption filters (colour filters) and dielectric filters.
|Physical Principle||Price||Power Handling||Angle Tolerance||Thickness||Dysfunctions||Reflection||RoHS-Conform|
|Absorption||Low||Heating due to absorption: may break at high power||Wide angle tolerance||Level of blocking depends on thickness. Typ. 2 – 3mm||May fluorescence when blocking UV light||Low||Many types “No” but with “legal” exeption status|
|Dielectric||High in small volumes. Low to mid in high volumes||Withstand high optical power due to low absorption||Functional spectrum blue shifts with angle||May be very thin eg 0.5mm||None||Low in transmission region. High in blocking region||Yes|
|Specifications||Absorption Filters||Dielectric Filters|
|Range of dimensions||1mm – 300mm||1mm – 300mm|
|Highest available surface figure||λ/4 (DIN: 3/0,5)||λ/4 (DIN: 3/0,5)|
|Highest available surface quality||40-20 S/D (DIN: 5/2×0,16)||40-20 S/D (DIN: 5/2×0,16)|
|Highest available tolerance of beam deviation||3” (arcsec)||3” (arcsec)|
|Blocking||—||OD3 (standard), OD5 (high blocking)|